The invention relates to a valve-controlled internal combustion engine including a cylinderhead with an outlet passage joined by a secondary air supply passage for supplying fresh air to the exhaust gas discharged from the engine through the outlet passage.
In order to reduce the emission of pollutants from internal combustion engines, it is known to feed secondary air to the exhaust gas system in order to burn carbon monoxide and hydrocarbon components of the exhaust gases in a thermal reactor or catalytic converter. U.S. Pat. No. 4,103,488 discloses a valve-controlled internal combustion engine in which secondary air is fed into an exhaust duct through a nozzle just downstream of an exhaust valve. A control valve is provided in the air supply line, which control valve is closed when the exhaust gas pressure is higher than the pressure in the air supply line and opens when the pressure in the exhaust gas duct drops. As a result, the air can flow out of the secondary air nozzle essentially only when the exhaust valve is closed. This considerably reduces the effectiveness of introducing secondary air into the exhaust gas.
German laid-open application DE-A 2 033 794 A discloses a method for detoxifying exhaust gases in spark ignition engines by post-combustion of the exhaust gases outside the engine. The exhaust gases are expanded in a swirl generator with adjacent diffuser and the combustion air is sucked in by the vacuum produced in the process. The post combustion takes place in the diffuser in which the pressure rises again. Such a method can be carried out only with increased structural expenditure.
DE 295 15 054 U1 discloses an exhaust gas detoxification system for internal spark ignition combustion engines on the basis of catalytic post-combustion in which a Venturi nozzle is arranged in such a way that the partial vacuum produced by an exhaust gas flow in the Venturi nozzle is used to introduce air into the stream of exhaust gas. In addition, it is proposed to integrate one or more non-return valves into the air feed line. However, an increased structural expenditure is also necessary for this solution.
It is the object of the invention to improve the feeding of secondary air into the engine exhaust duct by simple, inexpensive means.
In a valve-controlled internal combustion engine having a cylinderhead with an exhaust gas passage extending from a combustion chamber and a secondary air duct for supplying secondary air to the exhaust gas passage downstream of an exhaust valve opening, the exhaust gas passage includes a projection just downstream of the exhaust valve opening, which projection extends in the direction of flow of the exhaust gases and forms, with the exhaust passage wall, a pocket which is open towards the exhaust passage and into which the secondary air passage opens for supplying secondary air to the exhaust gas.
As the exhaust gas flows past the opening of the pocket at a high speed the secondary air is entrained into the stream of exhaust gas whereby the air is mixed intensively with the exhaust gases. Post-combustion reactions, which are finally completed in the exhaust gas catalytic converter thus occur even on the way to the catalytic converter.
The pocket is preferably funnel-shaped by virtue of the fact that the pocket widens at an acute angle xcex1 in the form of a funnel towards the exhaust gas passage in a first plane including the axis of the exhaust gas passage. Preferably, the pocket widens toward the exhaust passage at an acute angle xcex2 in a second plane normal to the first plane to form a discharge funnel. This increases the pressure of the secondary air towards the exhaust passage, as a result of which the secondary air can relatively easily be mixed into the exhaust gases flowing in the exhaust gas passage.
Further advantages will become apparent from the description of the invention on the basis of the drawings. An exemplary embodiment of the invention will be described with reference to the drawings.